Lift installations of that kind are known per se. Equally known per se is that in the case of installation or maintenance of a lift installation there is the threat of significant risks and accordingly precautions have to be taken in special mode and manner for the personnel tasked therewith, especially an engineer, who stands in the lift shaft. With regard to the prior art in this respect reference can be made to JP 2005-132543 A, U.S. Pat. No. 6,202,797 B and WO 2007/018540 A. Particularly risky areas in that case are the foot of the lift shaft (shaft pit) and the upper end of the lift shaft (shaft head).
A safety system is proposed in JP 2005-132543 A, U.S. Pat. No. 6,202,797 B and WO 2007/018540 A in which the engineer carries a wireless transmitter/receiver and at least one transmitter for wireless transmission of a signal is mounted on each of the lift cage and the counterweight. In the case of JP 2005-132543 A the receiver carried by the engineer receives a signal from a transmitter of the lift cage or the counterweight when the engineer approaches this and the engineer receives a warning report. By means of the transmitter carried by the engineer, a signal is transmitted in parallel to a receiver unit of the lift installation which is to cause the lift control to stop the movement of the lift cage. In the case of U.S. Pat. No. 6,202,797 B the engineer similarly carries a transmitter/receiver and, in particular, as part of his or her uniform. In the case of WO 2007/018540 A the engineer carries a safety device in the form of a headset. Disposed in the lift shaft and functioning, so to speak, as a movement reporting device is an ultrasonic transmitter/receiver which is to recognize the presence of an engineer in particularly risky areas, namely the foot and the upper end of the lift shaft. If the lift cage or the counterweight is in the vicinity of the engineer the safety device receives a warning signal by means of an ultrasonic receiver and as a consequence of the warning signal an acoustic warning report to the engineer is carried out by means of a loudspeaker included in the safety equipment. The circumstance of whether the lift cage or the counterweight is in the vicinity of the engineer is to be recognized by means of transmitter/receiver pairs arranged in the lift shaft and at the lift cage.
The previous safety systems seem capable of further improvement. The detection of an engineer by means of a movement sensor is susceptible to error and does not, for example, recognize an engineer when the engineer is carrying out a measurement and in that case does not move or hardly moves for some time. The approach presented in U.S. Pat. No. 6,202,797 B requires the engineer to wear his uniform at all times. In the case of JP 2005-132543 A the engineer similarly has to carry the transmitter/receiver.